A great variety of flowable products can advantageously be packaged in burstable pouches. Such pouches may contain a variety of liquids or other flowable materials. Examples include ketchup, mustard, salad dressings, certain photographic compositions, air fresheners, insecticides, water, skin lotions, soaps, and hair care products, to name just a few.
Likewise, burstable pouches may be used in different configurations. Most typically, a single pouch is formed having a burstable seal along one edge from which a stored product may be released for consumption or use. In other configurations, a burstable seal divides two chambers until the burstable seal is broken. In some cases a burstable pouch may be sealed within another larger pouch to form inner and outer chambers. In other cases, two adjacent chambers made of the same opposed flexible film sheets are separated by a burstable seal which joins the flexible films between the chambers such that the bursting therof gives one larger chamber.
When two-chambered pouch configuations are used, two chemical reactants may be stored separately in adjacent chambers. Upon bursting of the burstable seal, the contents of the two chambers intermix and/or react to produce some desired composition or effect. For example, separately stored water may thereby be mixed with dehydrated foodstuffs in an adjacent chamber.
In other cases, one chamber of a two-chamber configuration may be empty until it receives the contents of the other chamber upon bursting of the burstable seal. In the receiving chamber the contents will perform some function which was impossible in the first chamber. For example, an air-freshening liquid composition may be stored in a chamber made of impermeable plastic material, and upon breaking of the breakable seal flow into a chamber made of a permeable plastic material through which it may be dispensed over time to the surrounding atmosphere. See PCT Publication No. WO 82/02700.
A burstable pouch may burst by pre-intended breakage of a seal along one edge of the pouch. Such seal can break when the pouch is squeezed, while any remaining edge seals of such pouch are permanent and resist breakage. Many of such pouches are made of plastic films. It is burstable pouches of this type to which this invention is directed.
The prior art discloses a number of methods for forming breakable seals between two plastic films. In some cases, seams made by heat and pressure applied through constant-temperature heat sealing bars or impulse heat sealing are made breakable by the application of less heat and pressure than is normally used in making permanent seals and/or by reducing the width of the area to which the heat and pressure are applied. These methods of making breakable seals will often produce seams which are either too strong to be easily ruptured or too weak to maintain a satisfactory seal during normal handling. Seal inconsistency is a major problem.
The prior art discloses an improvement on such techniques, namely, the use of additional foam layers to form the breakable seal. See PCT Publication No. WO 82/02700. The imposition of foam layers in the formation of breakable seals fails to produce desired or even acceptable consistency of breakable seals. The strength and bursting qualities of such seals remain extremely sensitive to variations in the heat sealing steps, including, for example, the times, temperatures, and pressures involved.
Other methods for making breakable seals involve the use of chemical or mechanical inhibitors between the films to be sealed. A chemical inhibitor can prevent the formation of a permanent seal, giving instead a breakable seal, even though a heat sealing bar is applied for a time and at a temperature sufficient to make a permanent seal in the absence of such inhibitor. Mechanical inhibitors serve the same purpose by interrupting the seal. U.S. Pat. No. 3,074,544, for example, discloses the use of masking means such as porous fibrous webs to weaken heat seals. The quality of such breakable seals tends to vary unacceptably.
A variety of films have been used in standard pouch making and a variety of sealing techniques have been used to join together flexible plastic films into permanent seals. U.S. Pat. No. 3,770,122, for example, refers to the use of conduction, impulse, high frequency (RF) and ultrasonic welding methods, and mentions the use of laminates of various kinds. U.S. Pat. No. 3,770,122 is not at all concerned, however, with the formation of burstable seals.
Prior teachings relative to the formation of burstable pouches have failed to produce highly reliable breakable seals of consistent quality. The use of ultrasonic sealing techniques to seal together two laminated films, in which the contacting layers of the two films have a relatively low melting point and the remote layers have a relatively high melting point, fails to provide desired consistency in the breakable seals. U.S. Pat. No. 3,749,620 describes the use of ultrasonic sealing for this purpose. Such burstable seals, however, are not sufficiently consistent in their quality from package to package to be reliably used in many applications.
One disadvantage of ultrasonic welding in making breakable seals is that, when such ultrasonic seals intersect previously made permanent heat seals, the area of intersection is often weak and may be prone to leak. Furthermore, such ultrasonic seals are of necessity narrow in width and thus prone to be less consistent from pouch to pouch. The problem with ultrasonic sealing is that it tends to be destructive to the films at least to some extent, and this may lead to inconsistency in the seals.
A variety of modifications and adjustments have been made to basic welding methods for plastic films in order to acheive desirable qualities in a burstable pouch. Such methods have produced less than desirable results in pouch making for various applications.
All of the prior methods for making breakable seals for burstable pouches have significant drawbacks. There is a clear need for an improved method of forming closed burstable pouches having breakable seals of high consistency in strength and bursting qualities.